These days, earnest attention is being paid all over the world to nanotechnology for constructing a structure of a nanometer size. As one of the nanotechnology, an attempt is being made to form a metal nanoparticle by using, as a die, a protein in the shape of a spherical shell or a bar. Examples of the protein used in the so-called bio-nanoprocess are apoferritin, listeria ferritin and DNA binding protein.
FIG. 1 is a diagram for showing the characteristics of ferritin (apoferritin) and listeria ferritin (listeria apoferritin). Ferritin is a spherical shell-shaped protein included in a large amount in a liver, a spleen and a heart of a mammal with a diameter of approximately 12 nm (in a case of a horse), and 24 monomer sub-units 3 each including 175 amino acids together form one protein molecule. One protein molecule has a molecular weight of 480 kDa. The ferritin has, in vivo, a core 1 of iron oxide with a diameter of 7 nm at most within a shell 2 of the protein. Ferritin from which the iron oxide core 1 has been slipped off is designated as apoferritin.
On the other hand, the listeria ferritin is a Dps-like protein derived from Listeria monocytogenes, includes 12 monomer sub-units 9 and is in the shape of a spherical shell with a diameter of approximately 9 nm. In the listeria ferritin, a cavity where a core 6 of iron oxide can be held is formed within a shell 7 in the same manner as in the apoferritin, and the cavity has a diameter of approximately 4 nm. Listeria ferritin from which the tin oxide core 6 has been slipped off is designated as listeria apoferritin.
In the apoferritin, a core made of any of various metals can be formed instead of the iron oxide core. Therefore, complexes each composed of a nanoparticle of any of various metals such as cobalt (Co), manganese (Mn) and nickel (Ni) and the apoferritin have been conventionally produced. Also the listeria ferritin can be used in forming a nanoparticle of any of various metals.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-113198